Actually, I have been having this problem too. Mostly it happens when I try and put an away message up, but this morning it just booted me around 700am, and I tried to sign back on, and it said service couldn't be reached. I have 2 SNs, and was perfectly able to sign on with my other one, but not the one I use now. No one else in my building is haveing this problem either, so it's not the server or anything. Very freaky to me. FInally after 3 hours, I could put my real SN back on.
It did this to me about 3 weeks ago as well, I just uninstalled it, and reinstalled it, and it was all good, but it just started flaking on me again last weekend.